In reality, only one star blew up, but all the light coming from
the supernova was magnified and distorted by a bizarre phenomenon
called gravitational lensing.

Albert Einstein was the first to describe gravitational lensing,
and though he
couldn't believe it at the time, it predicts that massive
objects with intense gravitational pull — like a planet, galaxy,
or galaxy cluster — can dramatically bend and warp the fabric of
space itself:

Public
Domain

The gravitational field acts like a lens, bending and redirecting
light from background objects. So, depending on your vantage
point, smaller objects behind the big gravity field can appear
huge or even in multiple places at once.

Which is exactly what happened with a cluster of galaxies called
MACS J1149+2223.

The galaxy cluster is about 5 billion light-years away and, last
year, acted as a gigantic lens for a supernova behind it. The
supernova appeared in four different spots marked by arrows in
the image below — a phenomenon called an "Einstein cross."

You might notice that all four images don't look the same; that's
because the light is bent more in some images than
others. The more the light is bent, the longer it takes to
reach our telescopes:

NASA

Since astronomers first noticed it in November 2014, the
supernova has faded away. But now they're predicting
light from the same explosion will replay at a
different spot within the same gravitational
lens.

Their calculations,
published in a study on the preprint server arXiv, suggest
we'll see the supernova again sometime between January 2016
and April 2016.

This is a "once-in-a-lifetime" opportunity, according to a
Hubble
press release, to see how well we understand gravity lenses
and other advanced physics.

It may also be the first time ever we'll get to zero in on and
watch a star blow up from start to finish. That's huge, since
supernovas make all of the atomic elements essential for life,
yet we know very little about them.